1. Field of the Invention
This invention relates to furnaces, and particularly to the method and apparatus in a furnace for effectively incorporating an incandescent filter through which the products of combustion of the furnace must pass to convert such products of combustion into harmless non-toxic vapors.
2. Description of the Prior Art
A search for prior art in connection with this invention has been conducted in the following classes and sub-classes:
Class 126 and sub-classes 58, 67, 69, 75, 76, 103, 108, 110AA, 112, 152R, 193, 225; PA1 Class 110 and sub-classes 208, 209, 214, 236, 309, 315; PA1 Class 122 and sub-classes 162 and 204.
As a result of the search in the area indicated, and in reviewing the prior art in the form of patents that have been issued to companies that are active in the industry of manufacturing furnaces, and through a review of literature purchased through the National Technical Information Service of the United States Government, sixty patents are known to exist as follows:
______________________________________ 91,821 698,800 698,810 2,295,781 3,874,362 4,201,141 208,221 698,801 843,103 2,461,068 3,937,154 4,203,374 503,817 698,802 843,104 2,481,164 4,044,820 4,285,328 518,576 698,803 843,105 2,481,165 4,063,521 4,354,440 628,272 698,804 843,106 2,488,014 4,074,638 4,356,778 644,792 698,805 998,800 2,564,713 4,080,909 4,366,759 698,796 698,806 1,069,577 3,780,674 4,102,318 4,380,228 698,797 698,807 1,326,621 3,844,233 4,172,425 4,395,956 698,798 698,808 1,716,319 3,855,950 4,191,114 4,441,436 698,799 698,809 1,954,923 3,861,332 4,194,487 4,449,460 4,471,753 ______________________________________
The construction of stoves and furnaces, as we know them today in the form of appliances that are enclosed within a room or a building for the purpose of generating heat within that room or building, are of relatively recent origin. Historically, the term "stove" was used to define a room that was artificially heated in some way. The term was not utilized in early history to designate the device by which the room was heated.
As used today, the term "stove" is generally applicable to appliances most usually stationed and utilized in a kitchen, for purposes of heating and cooking. In most instances, stoves today are not used to provide illumination in a room, although there are exceptions to this general rule. Furnaces on the other hand, are an outgrowth of stoves, and appear to have evolved from fuel burning stoves when habitats changed from single rooms to multiple rooms and to multiple stories of rooms. In this latter case, the "stove", now stylized a "furnace", was moved into the basement of the house or habitat and was utilized through the use of appropriate fuel and grates or ducts to heat the entire house.
As our society advanced in technology, it became evident that the generation of heat was necessary to accomplish many of the technological processes that were being invented. Accordingly, the furnace as we know it today used in industrial environments evolved from the furnace that was first used to heat homes, which in turn was an outgrowth of the stove as an appliance that was used in early history for heating and cooking. History reveals to us that for many years the solid fuel burning stove, constituted almost the only type of heating appliance that was available. Through passage of time, and the discovery of natural gas, and other flammable gases and liquids, such as kerosene and oil, stoves and furnaces have evolved into more and more complex structures. For a time in recent history, the solid fuel burning stove and furnace as we know it, either for home heating or for industrial heating, has been almost replaced by oil and gas fired furnaces.
However, again because of recent history, and the increase of the price of oil and hydrocarbon type fuels, wood burning stoves and furnaces, and more broadly solid fuel type furnaces, have once again enjoyed considerable attention. However, almost coincidentally with the popularity of the solid fuel burning appliance has come the realization that the products of combustion of solid fuel appliances has a tendency to pollute the atmosphere with both visible and invisible contaminants. As a consequence, the Environmental Protection Agency in the United States has set down very specific quantitative and qualitative limits to the contaminants that may be emitted into the atmosphere by industrial and domestic stoves, furnaces, incinerators and other solid fuel burning appliances. For instance, the Department of Environmental Quality for the State of Oregon has mandated that all new wood burning stoves or fire place inserts must be certified by the State's Department of Environmental Quality. To secure certification for 1987, for instance, wood burning stoves with catalytic combusters cannot emit more than six grams of total particulates an hour. In 1988, Oregon's standards will prohibit the same stoves and inserts from emitting more than four grams per hour. The law also mandates that non-catalytic stoves must keep their emissions down to fifteen grams an hour during 1987, and nine grams per hour by 1988. By July 1, 1988, it is expected that the new regulations will provide a particulate emission ceiling for ordinary stoves at 8.5 grams per hour, decreasing to 7.5 grams per hour after July 1, 1990. For stoves fitted with catalytic combustors (a smoke afterburner that works much like an automobile's catalytic converter), particulate emissions levels would have to be as low as 5.5 grams per hour in 1988, 4.1 grams per hour by 1990.
While these regulations are apparently directed only to particulates, which generate visible emissions, it is argued that when particulate levels are reduced, so are other harmful pollutants, such as the invisible gases that normally accompany visible pollutants. Obviously, the brunt of the regulations is going to be felt by stoves and furnaces that utilize oxygen restricting devices to control burning, the result being an inefficient, smoldering fire that sends excessive levels of pollutants up the flue.
However, products of combustion are not the only kinds of pollutants that society must address. While it is extremely important that we have clean air to breathe, it is also extremely important that we have clean water to drink. In this respect, metropolitan areas have encountered increasing difficulty in finding accessible and economically feasible landfill locations for disposing of all of the garbage and refuse that is generated by their inhabitants. For instance, a great deal of effort has been expended in an attempt to find a suitable way of disposing of the garbage and refuse generated by society. One of the ways of disposing of such garbage and refuse is to burn the material and to utilize the heat from combustion to generate electricity, thus recouping the cost of manufacturing and building the necessary facilities to effect incineration of the garbage and refuse. The argument that is given by the proponents of incineration of garbage and refuse is that the landfill method of disposal pollutes the underground aquifers, thus polluting the underground water supply of society in a manner that is untenable. However, as discussed above, the problem of releasing contaminants into the atmosphere and thus polluting the air we breathe, is also an untenable circumstance that society must solve, and this is advanced by the opponents of incineration.
Accordingly, one of the objects of the present invention is to provide a furnace that burns solid fuel such as wood and coal, and even refuse and wet garbage in such a way that the products of combustion are forced to pass through an incandescent filter in such manner that the products of combustion are themselves combusted or converted into non-polluting and non-toxic emissions.
Another object of the invention is the provision of a furnace which may be modular in its concept and structure, being increased or decreased in size to satisfy the needs of the user.
A still further object of the invention is the provision of a furnace structure, particularly the combustion chamber thereof, which can burn any fuel with emissions of fly ash, nitrogen oxides and sulfur oxides and visible particulates (smoke) well within any clean air regulations.
One of the problems that has occurred in connection with forest waste products, and other combustible fuels that contain large percentages of non-combustibles such as dirt, rock and scrap metals, is that there is a tendency for the conventional furnace to be plugged by such non-combustible materials. Accordingly, it is another object of the present invention to provide a furnace that will accept large percentages of such non-combustibles in the fuel with which it is fired, without being plugged by such non-combustibles.
It frequently happens, that stoves and furnaces are designed to accommodate a particular type of fuel. Thus, gas burning or oil burning furnaces are not designed to accept solid fuel such as coal or wood or garbage or refuse. Accordingly, another object of the present invention is the provision of a furnace structure, particularly the combustion chamber thereof, which will burn all types of fuels, whether they be gases, liquids or solids with no prior processing of the fuel being required.
A still further object of the invention is the provision of a furnace which will produce combustion so efficient that no scrubbing, filtering, electrostatic or centrifugal cleaning of the flue gases is required.
It is notorious that when wet fuel is applied to a furnace or fire, a great deal of smoke results by products of combustion that are not combusted and which merely smolder. Accordingly, a still further object of this invention is the provision of a furnace which will accept dripping wet fuel and burn such dripping wet fuel at very high efficiency with no visible emissions discharged into the atmosphere.
In one aspect of the invention, it is an object to provide in a furnace a combustion chamber that is completely sealed against the escape of products of combustion therefrom except through a designated outlet, that outlet being covered within the furnace structure by an incandescent bed of coals that requires that all products of combustion pass through the incandescent bed of coals prior to reaching the exit from the firebox.
Still another object of the invention is the provision of a combustion chamber for a furnace in which the combustion chamber is lined with water-cooled tubes, the tubes on at least one wall of the combustion chamber being arranged to provide an exit for hot gases from the combustion chamber, the exit being related to the charge of fuel so that primary air is admitted to the combustion chamber above the charge of fuel, while secondary air is admitted to the combustion chamber from below the charge of fuel, thus forcing the fuel above the outlet to burn in a down draft manner while the fuel below the outlet burns in an updraft manner.
In a preferred form of the invention, particularly when solid fuel such as wood or coal is being burned, the coals formed from the burning wood or coal form a thick layer which constitutes an incandescent filter through which products of combustion must be drawn so as to fully combust any combustible particulate matter that has resulted from the initial combustion, and transform or convert harmful gases to non-toxic unharmful vapors. However, in situations where the fuel does not generally form a thick incandescent bed of coals, it is desirable nevertheless to provide an incandescent filter through which the products of combustion will nevertheless be drawn. Accordingly, it is a still further object of this invention to provide a combustion chamber for a furnace equipped with means for providing such a thick bed of incandescent carbonaceous material even though the fuel may constitute combustible material that normally does not form large coals.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described, since it may be embodied in various forms within the scope of the appended claims.